linux-kernel - Re: [PATCH 7/8] drm/qxl: Use drm_fb_helper deferred

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Date:	Thu, 21 Apr 2016 09:49:39 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Noralf Trønnes <noralf@...nnes.org>,
	dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
	laurent.pinchart@...asonboard.com, tomi.valkeinen@...com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/8] drm/qxl: Use drm_fb_helper deferred_io support

On Thu, Apr 21, 2016 at 09:41:34AM +0200, Daniel Vetter wrote:
> On Wed, Apr 20, 2016 at 09:04:38PM +0200, Noralf Trønnes wrote:
> > 
> > Den 20.04.2016 19:47, skrev Daniel Vetter:
> > >On Wed, Apr 20, 2016 at 05:25:28PM +0200, Noralf Trønnes wrote:
> > >>Use the fbdev deferred io support in drm_fb_helper.
> > >>The (struct fb_ops *)->fb_{fillrect,copyarea,imageblit} functions will
> > >>now be deferred in the same way that mmap damage is, instead of being
> > >>flushed directly.
> > >>This patch has only been compile tested.
> > >>
> > >>Signed-off-by: Noralf Trønnes <noralf@...nnes.org>
> > >>---
> > >>  drivers/gpu/drm/qxl/qxl_display.c |   9 +-
> > >>  drivers/gpu/drm/qxl/qxl_drv.h     |   7 +-
> > >>  drivers/gpu/drm/qxl/qxl_fb.c      | 220 ++++++++++----------------------------
> > >>  drivers/gpu/drm/qxl/qxl_kms.c     |   4 -
> > >>  4 files changed, 62 insertions(+), 178 deletions(-)
> > >>
> > >>diff --git a/drivers/gpu/drm/qxl/qxl_display.c b/drivers/gpu/drm/qxl/qxl_display.c
> > >>index 030409a..9a03524 100644
> > >>--- a/drivers/gpu/drm/qxl/qxl_display.c
> > >>+++ b/drivers/gpu/drm/qxl/qxl_display.c
> > >>@@ -465,7 +465,7 @@ static const struct drm_crtc_funcs qxl_crtc_funcs = {
> > >>  	.page_flip = qxl_crtc_page_flip,
> > >>  };
> > >>-static void qxl_user_framebuffer_destroy(struct drm_framebuffer *fb)
> > >>+void qxl_user_framebuffer_destroy(struct drm_framebuffer *fb)
> > >>  {
> > >>  	struct qxl_framebuffer *qxl_fb = to_qxl_framebuffer(fb);
> > >>@@ -527,12 +527,13 @@ int
> > >>  qxl_framebuffer_init(struct drm_device *dev,
> > >>  		     struct qxl_framebuffer *qfb,
> > >>  		     const struct drm_mode_fb_cmd2 *mode_cmd,
> > >>-		     struct drm_gem_object *obj)
> > >>+		     struct drm_gem_object *obj,
> > >>+		     const struct drm_framebuffer_funcs *funcs)
> > >There should be no need at all to have a separate fb funcs table for the
> > >fbdev fb. Both /should/ be able to use the exact same (already existing)
> > >->dirty() callback. We need this only in CMA because CMA is a midlayer
> > >used by multiple drivers.
> > 
> > I don't see how I can avoid it.
> > 
> > fbdev framebuffer flushing:
> > 
> > static void qxl_fb_dirty_flush(struct fb_info *info)
> > {
> >         qxl_fb_image_init(&qxl_fb_image, qdev, info, NULL);
> >         qxl_draw_opaque_fb(&qxl_fb_image, stride);
> > }
> > 
> > drm framebuffer flushing:
> > 
> > static int qxl_framebuffer_surface_dirty(...)
> > {
> >         qxl_draw_dirty_fb(...);
> > }
> > 
> > qxl_draw_opaque_fb() and qxl_draw_dirty_fb() differ so much that it's way
> > over my head to see if they can be combined.
> > Here's an online diff of the two functions:
> > https://www.diffchecker.com/jqbbalux
> 
> Imo nuke the fbdev one entirely. If it breaks then it's either a bug in
> your generic fbdefio code, or the qxl ->dirty implementation has a bug. It
> should work ;-)
> 
> Ok, slightly more seriously the difference seems to be that the fbdev one
> support paletted mode too. But since qxl has 0 pixel format checking
> anywhere I have no idea whether that's dead code (i.e. broken) or actually
> working. I guess keeping the split is ok, if we add a big FIXME comment to
> it that this is very fishy.

Ok, I read around a bit more. The only things qxl seems to support are
bits_per_pixel of 1, 24 and 32 (see qxl_image_init_helper). And drm has no
way to pass in 1 bpp images. And it doesn't support 8 bit paletted, which
is the only paletted thing drm supports.

So if you totally feel like I think we could add format checking for
DRM_FORMAT_XRGB8888 and DRM_FORMAT_RGB888 in qxl_framebuffer_init and then
rip out all that code. But that's a few more patches and probably should
be tested actually ;-)

FIXME plus explaing it all in the commit message is fine with me too.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch